The game is Codex Mortis (Steam).

“It’s pure TypeScript. I use PIXI.js for rendering, bitECS for the entity-component-system backend, and Electron to wrap it as a desktop app,” Crunchfest3 wrote. “The whole thing was vibe-coded with Claude Code (mostly Opus 4.1 and 4.5).” The art, meanwhile, was generated by ChatGPT, and the game’s animations “are a shader written by Claude Code.”